1. Field of the Invention
The present invention relates to a method of concealing a video signal when an incorrectable error is detected during recording and reproduction of or during transmission of a digital video signal, and to an apparatus for performing the method.
2. Description of the Prior Art
A video signal is generally divided into specific blocks, and is recorded and reproduced using a recording medium or transmitted through a transmission path, in such a manner that transmission errors occur that can be detected, but cannot be corrected. Supposing that one page of digital video data is composed of K fields (K being an integer), and that the data in two pages are divided to form blocks, a detected errors was, hitherto, concealed by replacment with a block in one page before a page including a block containing the detected error.
Supposing, in a high efficiency coding, or bit rate reduction, by forming the data in two pages into blocks, that the first page and the second page are combined, and the third page and the fourth page are combined. At the time of reproduction, if an error is detected in a block composed of pixels of the third page and pixels of the fourth page, the pixels are respectively replaced with the pixels at the same positions on the screen of the second page. In a case of a still image, the pixels of the third page may be replaced by the pixels at the same positions of the first page, and the pixels of the fourth page by the pixels at the same positions of the second page. Since the video signal is very high in correlation between pages, it is possible to reproduce a block having a detected error by such concealing.
In this constitution, however, when the video signals are processed in two pages, if an error is detected, there exists a portion of no picture change over three or four pages. Accordingly, in a video signal having a large amount of motion, a significant degradation of picture quality arises, and on the moment of changing the scenes, in particular, the previous picture overlays on the new picture.